The U.S. Harmony node flew to space aboard space shuttle Discovery during mission STS-120, in October 2007. NASA describes Harmony as a "utility hub," as it circulates air, water, electrical power and similar systems to other space station modules. It supports the U.S. Destiny laboratory, the European Space Agency Columbus Laboratory and the Japanese Kibo laboratory.
Interior of Harmony
Harmony is a popular location to perform scientific experiments, too. You can see here — in a November 2013 mission — NASA astronaut Michael Hopkins doing a session with the Capillary Flow Experiment (CFE-2) during Expedition 38. Fluids behave differently in microgravity, and investigators are trying to learn more about that behavior to better design water and fuel delivery systems in newer spacecraft.
Most U.S. experiments take place aboard the U.S. Destiny Laboratory. Its work, according to NASA, supports "a wide range of experiments and studies contributing to health, safety, and quality of life for people all over the world." A typical space station crew will manage about 200 experiments during their six-month stay, covering topics ranging from health to manufacturing to life science experiments. Destiny launched in February 2001 aboard space shuttle Atlantis, during mission STS-98.
Interior of Destiny
Even a quick glance at the interior of Destiny shows the range of work going on in terms of U.S. experiments. This picture was taken early in Destiny's lifetime, in August 2003.
Here's an exterior view of the Cupola module, which was mentioned earlier in this slideshow while talking about Tranquility Node 3. The Cupola has a cover that astronauts can deploy or retract as required; keeping the cover closed protects the Cupola from micrometeorites, while keeping it open allows the astronauts to perform Earth observations.
Interior of Cupola
As shown in this Expedition 34 picture in 2012, the Cupola module has a bunch of equipment at the ready for astronauts to observe Earth — including multiple cameras. The module is designed to be always facing the Earth, providing astronauts the chance to do observations during night or day (as required). Astronauts can also set up cameras to automatically take footage as they perform other experiments on the space station.
The European Space Agency's Columbus Laboratory launched to space aboard space shuttle Atlantis in February 2008, as part of shuttle mission STS-122. Columbus is a facility where investigators on Earth (with the help of astronauts) can do experiments in the weightless environment of space, NASA says. Experiments can even be mounted outside of the space station on one of four exterior mounting platforms.
Interior of Columbus Laboratory
Here's a glimpse of a science experiment in progress inside of Columbus, in May 2017. Expedition 52's Jack Fischer puts on thigh and calf guides to prepare for ultrasound operations for an experiment called Integrated Resistance and Aerobic Training (Sprint). Helping him is Expedition 52 commander Peggy Whitson.
Bigelow Expandable Activity Module
This is an artist's concept of Bigelow Aerospace's Bigelow Expandable Activity Module (BEAM). This is an experimental module attached to the space station where NASA and Bigelow are learning more about how inflatable modules behave in space over long periods of time. Inflatable modules are easier to package and lighter to launch, providing a potential alternative structure for future space stations; however, it is unclear how the inflatable structure will hold up after long periods exposed to space radiation. BEAM launched to space in 2016 aboard the SpaceX Falcon 9 rocket and is now in an extended mission expected to last until at least 2020, according to NASA.
Interior of BEAM
Astronauts enter BEAM on occasion to take air samples and to inspect the structure for any changes. One such visit took place in February 2017, with Expedition 50 NASA astronaut Peggy Whitson (left) and European Space Agency astronaut Thomas Pesquet.